As described in U.S. Pat. No. 4,778,018, vibrating tray scales have been developed wherein flat articles (flats) such as letter mail, are conveyed onto the tray, or platform, of the scale. After a flat article has been conveyed onto the platform, the conveying mechanisms are withdrawn from the path of the flat article, the platform is unlocked so that it is free to vibrate, the flat article is held firmly against the platform and the platform is actuated to vibrate. A transducer is connected to a flexible member that supports the platform and, based upon the amount of vibration, the weight of the article can be determined. After the weight is determined, the platform is locked once more, the driving mechanism engages the flat article and the flat article is driven away from the scale.
An extensive amount of development has taken place with the vibrating tray scale first disclosed in 4,778,018, as shown in U.S. Pat. Nos. 4,856,602, 4,848,492, 4,836,311, and 4,844,188 among others. With such a scale, one is able to weigh two flats a second with accuracy to 0.001 ounces. Although the scales have operated in a most satisfactory manner, there has been one area in which constant improvement has been sought and this is the article transportation mechanism. As one might imagine, in a conveying mechanism of this type, wear is always a problem. When one is to weigh two articles a second clearly one operates the mechanism a large number of times within a short period. For example, in one day's processing of mail pieces, it is not unusual for a scale of the type described to perform 10,000 times. Over a period of a few months, clearly quit a bit of wear occurs either on the rollers or on a belt trained about the rollers as described in U.S. Pat. No. 4,856,602. It therefore would be advantageous to provide a drive mechanism that can be easily replaced, and which will perform its operations faster and in a quiet, smooth manner.